The invention relates to the field of hand tools and more particularly to the field of power drills, and even more particularly to hand-held power drills that can store multiple drill bits or other rotary tool bits internally in a rotatable magazine for selective use.
The conventional hand-held power drill has been a simple and generally effective tool for occasional use. The portable drill typically known to the art has a three jaw chuck assembly, with or without a chuck key, in which a selected tool bit is loaded for use from a remote storage container. After completion of a drilling or driving task, the tool bit is removed and returned to the storage container. The drilling task is then repeated using another, different, tool bit if required.
A compelling need for more efficiency in construction and assembly contexts has forced a re-evaluation of the time wasted in the selection, loading, unloading and general handling of tool bits. Some drill users employing conventional devices have resorted to the use of dedicated drill bit units to save time. Dedicating a drill to one tool bit is more efficient than repeatedly changing bits, but requires the higher capital investment of purchasing multiple drills where one will do. Dedicated drills also increase workplace clutter, and involve the time to put one unit down to search for and employ another unit.
Previous attempts have been made to solve the aforementioned problems. For example, as illustrated in U.S. Pat. No. 5,065,498 to McKenzie, it has been proposed to use a hook in the drill unit which engages an annular groove of a bit element holder upon manual manipulation of a bolt assembly with a cylindrical magazine to load/unload a bit element. The McKenzie device, however, requires specially machined bit element holders for every size of bit element, which increases the cost of the drill, and limits the variety of bit elements that can be used. Furthermore, a lack of visual reference of individual tool bit elements frequently requires a user to load and unload bit elements to find the desired bit. Because the bit-carrying bores of the McKenzie device are closed, dirty bits stored therein can not be cleaned without unloading the magazine. The inability easily to clean bits eventually will cause the drill to malfunction due to debris falling from the uncleaned bits into the motor and switch.
Another example of previous effort in the field is U.S. Pat. No. 5,346,453 to River-Bottzeck. The River-Bottzeck device uses a cylindrical tool bit magazine which has a very limited view port near the shank portion of the bit elements. Viewing only portions of bit shanks, however, makes positive identification of each bit almost impossible, and again an unload/load search may be required to find the correct bit element. Additionally, the tool bit bores of the Rivers-Bottzeck device can not be cleaned after a dirty bit element is re-inserted therein. The resulting inability to access and clean a bit immediately after use causes the drill to malfunction over time, due to debris eventually falling from the magazine into the drill motor and switch.
Also, most known multiple bit drill devices do not provide for a torque control device to prevent damage to the drill drive system. Some known non-multiple bit or "non-magazine" drills control torque range through the use of a multiple-step electronic control to shut off the motor when the voltage drop across the motor exceeds a preselected limit. To our knowledge, this type of solution has only been adopted in non-magazine drills. Because of the unique power train requirements of magazine type drills, however, selective torque control is not available in known devices. The device disclosed in the '498 patent to McKenzie does not provide any method for torque control, and the device of the '453 patent to Rivers-Bottzeck provides torque protection for the chucking mechanism only. The '498 patent to McKenzie and the '453 patent to Rivers-Bottzeck are believed fairly to represent the state of the art of multiple-bit portable drills, and the entire disclosure of each of those patents respectively is incorporated herein by reference.